99 accord - alternator or regulator?

My 99 Accord V6 has and electrical problem at idle speed. Headlights,
wipers, interior lights - everything dims or slows down when the car is
idling. When the engine revs just a little, everything returns to
normal. There's also a little bit of a whine I can hear while the
problem is happening.

The battery did test low and due to its age it probably needed
replacing. So I replaced it. But low-rpm voltage is still low. The
problem still exists.

I've got my eye on replacing the alternator, but I understand there's
also a voltage regulator part that tells the alternator when/how much/if
to charge.

How can I figure out what the problem is without throwing darts with my
money?

 

If I'm not mistaken the regulator is internal on your alternator. In any
event, the symptoms are consistent with a bad alternator.

The real tests are done with a digital voltmeter across the battery. The DC
voltage should be between 13 and 16 volts (low part of the range in hot
under-hood temperatures, high part of the range when cold). The voltage
should not change significantly when the engine is revved from idle. The AC
voltage should be under 0.1 VAC.

If the voltage is above 16 volts, the regulator is bad. If the voltage is
low at idle but comes up to spec when the engine is revved a bit, that is a
bad sign for the alternator. If the AC voltage is just above 0.1 volts, the
battery is not in good shape (your new battery should not show much AC
voltage at all unless the alternator is bad). If the AC voltage is more like
0.5 volts or more, you can be certain you have bad diodes in the alternator.

My prediction - you will have the low voltage coming up to normal as you rev
the engine, and high AC voltage across the battery... a definite bad
alternator. Anyway, that's what the whine leads me to suspect.

Beware of aftermarket alternators - they have earned a bad reputation for
reliability.

Mike

 

If I'm not mistaken the regulator is internal on your alternator. In any
event, the symptoms are consistent with a bad alternator.

The real tests are done with a digital voltmeter across the battery. The DC
voltage should be between 13 and 16 volts (low part of the range in hot
under-hood temperatures, high part of the range when cold). The voltage
should not change significantly when the engine is revved from idle. The AC
voltage should be under 0.1 VAC.

If the voltage is above 16 volts, the regulator is bad. If the voltage is
low at idle but comes up to spec when the engine is revved a bit, that is a
bad sign for the alternator. If the AC voltage is just above 0.1 volts, the
battery is not in good shape (your new battery should not show much AC
voltage at all unless the alternator is bad). If the AC voltage is more like
0.5 volts or more, you can be certain you have bad diodes in the alternator.

My prediction - you will have the low voltage coming up to normal as you rev
the engine, and high AC voltage across the battery... a definite bad
alternator. Anyway, that's what the whine leads me to suspect.

Beware of aftermarket alternators - they have earned a bad reputation for
reliability.

Mike

 

Before you spend all your money- Check the grounds. The symptoms you
describe could be from bad grounding.

-Pete

 

Before you spend all your money- Check the grounds. The symptoms you
describe could be from bad grounding.

-Pete

 

Are you sure the alternator drive belt isn't slipping? Had your
symtoms in a Datsun truck, no belt chirping to tip me off it was
loose.


Tom Willmon
near Mountainair, (mid) New Mexico, USA

Some days the only good thing on TV is the vase.

Net-Tamer V 1.12.0 - Registered

 

Are you sure the alternator drive belt isn't slipping? Had your
symtoms in a Datsun truck, no belt chirping to tip me off it was
loose.


Tom Willmon
near Mountainair, (mid) New Mexico, USA

Some days the only good thing on TV is the vase.

Net-Tamer V 1.12.0 - Registered

 

ive replaced dozens of those 98-02 v6 accord alts. first they start making
noise, then they stop charging. you'll know by the smell. they go out more
often than ive ever seen on any other vehicle. if you do it yourself,
there's 2 ways you can get it out of the engine bay. good luck.

 

ive replaced dozens of those 98-02 v6 accord alts. first they start making
noise, then they stop charging. you'll know by the smell. they go out more
often than ive ever seen on any other vehicle. if you do it yourself,
there's 2 ways you can get it out of the engine bay. good luck.